Manga is different from English comics in nuance, and refers to a (monochrome) line drawing having feels unique to Japan. When manga is printed in the form of publications, monochrome printing is predominant because color printing is costly. Thus, expressions in black and white such as various tones, shading, effect lines, solid, and the like have been accomplished for the expression of gradation and the expression of feelings.
However, the number of sites on which manga in the form of electronic data can be read on portable telephones has recently been increasing rapidly. This has provided more opportunities to appreciate manga on liquid crystal monitors, and there has been a growing demand for the coloring of (the application of color to) manga. Since there is little culture of monochrome manga outside Japan, the coloring of manga is necessary for the purpose of internationally expanding manga in the form of publications outside Japan. For these reasons, the operation of applying color has been required for the conversion of manga expressed by a line drawing image into electronic data.
A technique, for example, to be described below is disclosed to make the application of color to a line drawing image easy and convenient.
Patent Document 1: Japanese Patent Application Laid-Open No. 2007-220056
Useful in applying color to a line drawing image is an image layer process. An image layer is treated as an imaginary transparent sheet. Displaying a line drawing image desired to be colored as a plurality of image layers allows the individual application of color to the image layers. The application of color to each of the image layers facilitates modifications and re-application of color. Also, effects such as shadowing can be easily changed by changing the order in which the image layers are superimposed.
In general, when the image layer process is performed, a plurality of copies of a line drawing are treated as image layers, and the color application process is performed on each of the plurality of image layers. By collecting the image layers subjected to the color application process, a single line drawing image to which color is completely applied can be obtained.
However, in the application of color to the line drawing image by the use of such an image layer process, the operation per se of applying color to each of the image layers includes the process of pouring color into a portion desired to be colored or the process of manually applying color to the portion desired to be colored after the desired portion is displayed on an enlarged scale in a manner similar to the conventional technique of applying color to the line drawing image. This presents a problem in that the operation of applying color is laborious.
Also, there has recently been proposed a technique in which a closed region desired to be colored is extracted from a plurality of closed regions constituting an image represented by a line drawing, and color is poured into the desired closed region. In this case, the color application process is performed after the closed region desired to be colored is extracted. This achieves the color application process with efficiency without color application errors.
In the application of color to manga, however, there are a large number of closed regions constituting a character that is an image represented by a line drawing, and the closed regions are complicated in shape. This presents a problem in that it is difficult to extract a desired closed region. As an example, there are cases where a single component representing a character is composed of a plurality of closed regions, such as in the representation of hair. In this case, hair is represented by a plurality of closed regions although there is a single region as “hair.” It is hence necessary to perform the process of applying color to the plurality of closed regions constituting hair when applying color to hair. For this reason, improvements in the efficiency of the color application process by the use of the conversion into the closed regions cannot be accomplished.